Non Patent Literature (NPL) 1 discloses a specification for a function known as CS (Circuit Switched) fallback that implements cooperation between LTE (Long Term Evolution) and a 3G circuit switching service. Furthermore, the article “4.3.2 MME” of page 11 of the same literature discloses that, in a case of a configuration of an MSC/VLR (Mobile Switching Center/Visited Location Register) pool where a plurality of MSC/VLRs provide service with the same Location Area Identity, an MME (Mobility Management Entity) is to select a MSC/VLR by an IMSI Hash method of Non Patent Literature 2. It is to be noted that the IMSI Hash method is a method to obtain a hash by a modulo operation, with an IMSI (International Mobile-Station Subscription Identifier) that is an identifier for uniquely identifying a subscriber within a network and the number of MSC/VLRs inside a network as two keys.
Patent Literature (PTL) 1 discloses that when UE (User Equipment) initially accesses an SGSN (Serving GPRS Support Node) pool or the like, a RAN node such as an e-NodeB selects a suitable CN (Core Network) node for the UE in accordance with a NNSF (Non Access Stratum Node Selection Function) and a load splitting (distribution) rule. In addition, Patent Literature 1 discloses that a RAN node finds and selects a CN (Core Network) node where the UE is originally registered, by using an NRI (Network Resource Identifier) inside a TMSI (Temporary Mobile Station Identifier) included in an initial direct forwarding message received by the UE. That is, as long as the UE of Patent Literature 1 moves within a pool, the CN node does not change.
Patent Literature 2 discloses an MME in which, for the MME where a tracking area update request (TAU request) from a UE is converted to a location area update request (LAU request), a location area update response (LAU response) including an NRI is received from an MSC and is converted to a tracking area update response (TAU response) for the UE.